@Data
public class Message {
    private String title;
    private String message;
}

@Configuration
public class MailConfig {

    @Value("${spring.mail.host}")
    private String host;

    @Value("${spring.mail.username}")
    private String username;

    @Value("${spring.mail.password}")
    private String password;

    @Value("${spring.mail.port}")
    private int port;

    @Value("${spring.mail.protocol}")
    private String protocol;

    @Value("${mail.debug}")
    private String debug;

    @Bean
    public JavaMailSender getMailSender() {
        JavaMailSenderImpl mailSender = new JavaMailSenderImpl();

        mailSender.setHost(host);
        mailSender.setPort(port);
        mailSender.setUsername(username);
        mailSender.setPassword(password);

        Properties properties = mailSender.getJavaMailProperties();

        properties.setProperty("mail.transport.protocol", protocol);
        properties.setProperty("mail.debug", debug);

        return mailSender;
    }

}

@Service
@RequiredArgsConstructor
public class MailSenderService {

    private final JavaMailSender mailSender;

    @Value("${spring.mail.receiver}")
    private String emailTo;

    @Value("${spring.mail.username}")
    private String emailFrom;

    private void send(String subject, String message) {
        SimpleMailMessage mailMessage = new SimpleMailMessage();

        mailMessage.setFrom(emailFrom);
        mailMessage.setTo(emailTo);
        mailMessage.setSubject(subject);
        mailMessage.setText(message);

        mailSender.send(mailMessage);
    }

    public void sendMessage(String title, String message) {
        if (!(StringUtils.isEmpty(title) && StringUtils.isEmpty(message))) {
            String msg = String.format(
                    "Andrew, you have got message, title: %s, message: %s",
                    title, message);

            send(title, message);
        }
    }
}

@PostMapping("/send")
    public String sendMessage(Message msg, Model model, BindingResult bindingResult) {
        if (bindingResult.hasErrors()) {
            return "main";
        }
        model.addAttribute("msg", msg);

        mailService.sendMessage(msg.getTitle(), msg.getMessage());

        return "main";
    }

<h1>Send me a message on e-email</h1>
<form action="/send" th:action="@{/send}" th:object="${msg}" method="post">
    <p>
        <label>Title:
            <input type="text" th:field="${msg.title}"/>
        </label>
    </p>
    <p>
        <label>Message:
            <input type="text" th:field="${msg.message}"/>
        </label>
    </p>
    <p>
        <input type="submit" value="Submit"/>
        <input type="reset" value="Reset"/>
    </p>
</form>

spring.mail.receiver=

spring.mail.host=smtp.gmail.com
spring.mail.username=
spring.mail.password=
spring.mail.port=465
spring.mail.protocol=smtps
mail.debug=false